1. Field of the Invention
The present invention relates in general to insulating covers for liquid baths, and more specifically to the use of hollow interior, discrete particles for forming such a cover.
2. Description of the Prior Art
In many industries it is often necessary to make use of heated process baths utilizing large open liquid surfaces. Solid covers are not practical for use on these baths because it is essential to have ready access to the heated liquid. Yet such baths must be continually maintained at elevated temperatures and are both inefficient and unpleasant to work with because of the loss of heat to the surrounding environment. In addition, they frequently produce unpleasant or toxic vapors which may be a health hazard and also corrode surrounding structures and equipment.
Heretofore, attempts have been made to alleviate the deficiencies of open heated baths with the use of floating expanded vermiculite, carbon, flyash, or polymeric beads on the liquid surface.
Although expanded vermiculite is a good insulator, it is unsuitable in most heated bath applications because it readily wicks many liquids, especially water and molten salt, and sinks to the bottom of the bath. It has also been reported that vermiculite reacts with molten salt to form a sticky, difficult to remove, tar-like substance on the bath surface.
The use of floating granulated carbon also has not proved to be a solution because it either burns in air at elevated temperatures or eventually sinks in lower specific gravity liquids. In the case of molten salt baths, it has been reported that the build up of carbon (which is an electrical conductor) causes short circuiting and premature failure of expensive electrodes. Carbon also presents a serious fire safety hazard if it is dragged into high temperature quench baths containing nitrate or nitrite salts. Carbon is also very dirty to work with and can be difficult to remove from parts.
The use of high surface area flyash base products has not been satisfactory, particularly in molten salt baths, because it often results in the formation of a rigid, difficult to penetrate cover due to salt readily wicking into the high surface area flyash and solidifying. Also, higher density ash particles eventually sink after they have become wetted resulting in rapid sludge formation at the bottom of the bath.
The use of polymeric balls to form a floating insulating cover is limited by their relatively high cost, chemical reactivity and low temperature capability; currently marketed polypropylene balls are limited to a temperature of approximately 120.degree. C.
The present invention relates to the use of hollow interior ceramic particles to form a floating insulating cover that overcomes the drawbacks and problems that the prior art processes possess and provides an effective easily used heat insulating process.